What are moon phases and why do they occur?

Answer 1

The moon doesn't produce it's own light, it reflects light from the sun. When the moon orbits the earth every month one half of the moon's disk is always lit up by the sun, while the other half is always in darkness. The moon also rotates on it's axis every month, but as it revolves around the Earth only one hemisphere of the moon faces us - this is called the near side.

The eight phases of the moon are:

1. New Moon - this is when the moon is in the same direction of the sun, during this phase the far side of the moon (the bit we don't see) is fully illuminated and the near side of the moon is in complete darkness so it can't be seen from Earth. It rises and sets at about the same time as the sun.

2. Waxing crescent - this is when the moon has revolved around Earth far enough (after a day or two) that a slim portion of the moon's near side can be seen, it looks like banana-shaped from Earth. It rises some time after sunrise and sets between sunset and midnight.

3. First Quarter - during the First Quarter moon phase, one half of the moon is visible to us on Earth (either the right side or the left side of the moon will be visible depending on the viewer's location). It rises around lunchtime and sets at about midnight.

4. Waxing Gibbous - during this moon phase, more than one half of the moon's illuminated side can be seen from Earth, it is sort of egg-shaped when viewed from Earth. This moon rises just before sunset and sets just before sunrise.

5. Full Moon - The moon has completed one half of it's journey around the Earth, during this moon phase, the near side of the moon is in complete sunlight and the far side of the moon is in complete darkness so it looks like a complete circle from Earth. The Full Moon rises at sunset and sets at sunrise, being above the horizon the entire night.

6. Waning Gibbous - during this moon phase, more than half of the sunlit side of the moon is visible to viewers on Earth, but the less of the moon can be seen (this is said to be waning). The Waning Gibbous moon rises shortly after sunset and sets shortly after sunrise.

7. Third Quarter - the moon has completed three quarters of it's journey around the Earth. One half of the moon can still be seen from Earth. This moon phase rises at midnight and sets around lunchtime.

8. Waning Crescent - the last and final phase before the next New Moon is the Waning Crescent moon, during this moon phase, an observer on Earth can see less and less of the moon's sunlit side each day until it vanishes at the time of the following New Moon. It rises between midnight and sunrise and sets between midday and sunset.

To finish off the subject, lets talk about eclipses. During the New Moon phase, the moon sometimes passes directly in front of the sun blocking out the sun's light, this is called a solar eclipse. During the Full Moon phase, the moon sometimes passes through the Earth's shadow at night taking on a reddish brown color, and this is known as a lunar eclipse.